JP2011222989A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device including an oxide semiconductor, which has stable electric characteristics and high reliability.SOLUTION: In a transistor including an oxide semiconductor film, a metal oxide film is formed, and heat treatment is performed, the metal oxide film being in contact with the oxide semiconductor film, covering a source electrode and a drain electrode and having an antistatic function. Through the heat treatment, impurities such as hydrogen, moisture, a hydroxyl group, or a hydride are intentionally removed from the oxide semiconductor film, so that the oxide semiconductor film is highly purified. Further, by providing the metal oxide film, a parasitic channel is prevented from being generated on the back channel side of the oxide semiconductor film in the transistor is prevented.

Description

The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.

Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

A technique for forming a transistor (also referred to as a thin film transistor (TFT)) using a semiconductor thin film formed over a substrate having an insulating surface has attracted attention. The transistor is widely applied to electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a semiconductor thin film applicable to a transistor, but an oxide semiconductor has attracted attention as another material.

For example, a transistor using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) with an electron carrier concentration of less than 10 ¹⁸ / cm ³ is disclosed as an active layer of the transistor. (See Patent Document 1).

JP 2006-165528 A

However, the electrical conductivity of an oxide semiconductor changes when a shift from the stoichiometric composition due to excess or deficiency of oxygen or the entry of hydrogen or moisture to form an electron donor occurs in the thin film formation process. End up. Such a phenomenon becomes a variation factor of electrical characteristics for a transistor including an oxide semiconductor.

In view of such problems, an object is to provide a semiconductor device including an oxide semiconductor with stable electrical characteristics and high reliability.

Another object is to prevent the generation of a parasitic channel on the back channel side of the oxide semiconductor film.

In order to suppress fluctuations in the electrical characteristics of a transistor using an oxide semiconductor film, impurities such as hydrogen, moisture, hydroxyl groups, or hydrides (also referred to as hydrogen compounds) that cause fluctuations are intentionally excluded from the oxide semiconductor film. In addition, by supplying oxygen which is a main component material of the oxide semiconductor which is simultaneously reduced by the impurity removal step, the oxide semiconductor film is highly purified and electrically i-type (intrinsic).

An i-type (intrinsic) oxide semiconductor is an i-type by removing hydrogen which is an n-type impurity from an oxide semiconductor and purifying it so that impurities other than the main component of the oxide semiconductor are contained as much as possible. It is an (intrinsic) oxide semiconductor or an oxide semiconductor close to i-type (intrinsic). That is, the impurity is not made i-type by adding impurities, but by removing impurities such as hydrogen and water as much as possible, it is characterized by being highly purified i-type (intrinsic semiconductor) or approaching it. By doing so, the Fermi level (Ef) can be made to the same level as the intrinsic Fermi level (Ei).

In a transistor including an oxide semiconductor film, an oxide layer having an antistatic function is formed in contact with the oxide semiconductor film, and heat treatment is performed.

The oxide layer having an antistatic function is preferably provided on the back channel side (opposite to the gate insulating film) of the oxide semiconductor film, preferably a highly purified oxide semiconductor film. In addition, the oxide layer having an antistatic function preferably has a dielectric constant smaller than that of the oxide semiconductor. For example, an oxide layer having a dielectric constant of 8 to 20 is preferably used.

The oxide layer is thicker than the oxide semiconductor film. For example, it is preferable that the thickness of the oxide semiconductor film be greater than or equal to 3 nm and less than or equal to 30 nm, and the oxide layer be greater than 10 nm and greater than or equal to the thickness of the oxide semiconductor film.

As the oxide layer, a metal oxide can be used. As the metal oxide, for example, gallium oxide or gallium oxide added with 0.01 to 5 atomic% of indium or zinc can be used.

An oxide semiconductor film can be made highly purified by intentionally removing impurities such as hydrogen, moisture, a hydroxyl group, or hydride (also referred to as a hydrogen compound) from the oxide semiconductor film by a heating step. preferable. By the heat treatment, hydrogen or a hydroxyl group that is an impurity can be easily removed as water.

In addition, since heat treatment is performed in a state where the metal oxide film containing oxygen and the oxide semiconductor film are in contact with each other, oxygen which is one of the main components of the oxide semiconductor that is reduced at the same time by the impurity removal step Can be supplied from the metal oxide film containing oxygen to the oxide semiconductor film. Therefore, the oxide semiconductor film is more purified and electrically i-type (intrinsic).

In addition, after the heat treatment, a protective insulating layer that blocks entry of impurities such as moisture and hydrogen from the outside may be formed over the metal oxide film so that the oxide semiconductor film does not re-enter the oxide semiconductor film. .

A transistor including a highly purified oxide semiconductor film hardly shows temperature dependency in electrical characteristics such as threshold voltage and on-state current. In addition, there is little variation in transistor characteristics due to light degradation.

As described above, a transistor including a highly purified and electrically i-type (intrinsic) oxide semiconductor film is electrically stable because variation in electrical characteristics is suppressed. Thus, a highly reliable semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided.

The temperature of the heat treatment is 250 ° C. or higher and 650 ° C. or lower, or 450 ° C. or higher and 600 ° C. or lower, or less than the strain point of the substrate. The heat treatment may be performed in an atmosphere of nitrogen, oxygen, ultra-dry air (air with a water content of 20 ppm or less, preferably 1 ppm or less, preferably 10 ppb or less), or a rare gas (such as argon or helium).

One embodiment of the structure of the invention disclosed in this specification includes a gate electrode, a gate insulating film covering the gate electrode, an oxide semiconductor film in a region overlapping with the gate electrode over the gate insulating film, and an oxide semiconductor film. A semiconductor device includes a source electrode and a drain electrode that are in contact with each other, and a metal oxide film that is in contact with the oxide semiconductor film and covers the source electrode and the drain electrode.

In the above structure, a gallium oxide film is preferably used as the metal oxide film. The gallium oxide film can be obtained by sputtering, CVD, vapor deposition or the like. Although depending on the composition ratio of oxygen and gallium, the gallium oxide film has a band gap of about 4.9 eV and has translucency in the visible light region.

In this specification, gallium oxide may be expressed as GaOx (x> 0). For example, when GaOx has a crystal structure, Ga ₂ O ₃ where x = 1.5 is known.

In the above structure, the metal oxide film is preferably formed of a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc. In addition, the difference between the band gap of the metal oxide film and the band gap of the oxide semiconductor film is preferably less than 3.0 eV.

The oxide semiconductor film preferably includes indium and gallium.

In the above structure, the source electrode and the drain electrode preferably include a conductive material having a work function of 3.9 eV or more. The conductive material having a work function of 3.9 eV or more is preferably tungsten nitride or titanium nitride.

In one embodiment of the present invention, a gate electrode is formed over a substrate, a gate insulating film is formed to cover the gate electrode, and an oxide semiconductor film is formed in a region overlapping with the gate electrode through the gate insulating film. In this method, a source electrode and a drain electrode are formed over an oxide semiconductor film, a metal oxide film covering the oxide semiconductor film, the source electrode, and the drain electrode is formed, and heat treatment is performed.

In the above structure, a film containing gallium oxide is preferably formed as the metal oxide film. Further, it is preferable to form a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc as the metal oxide film. The temperature of the heat treatment is preferably 450 ° C. to 600 ° C.

In one embodiment of the present invention, a metal oxide film is formed in contact with the oxide semiconductor film, and heat treatment is performed. By this heat treatment, impurities such as hydrogen, moisture, a hydroxyl group, or hydride are intentionally removed from the oxide semiconductor film, and the oxide semiconductor film can be highly purified. A transistor including an oxide semiconductor film which is highly purified and electrically i-type (intrinsic) is electrically stable because variation in electrical characteristics is suppressed.

Thus, according to one embodiment of the present invention, a transistor having stable electric characteristics can be manufactured.

According to one embodiment of the present invention, a semiconductor device including a transistor with favorable electric characteristics and high reliability can be manufactured.

8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. FIG. 9 illustrates an electronic device. FIG. 9 illustrates an electronic device. (A) Model diagram showing laminated structure of dielectric, (B) Equivalent circuit diagram.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

In addition, the ordinal numbers attached as the first and second are used for convenience and do not indicate the order of steps or the order of lamination. In addition, a specific name is not shown as a matter for specifying the invention in this specification.

(Embodiment 1)
In this embodiment, one embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. In this embodiment, a transistor including an oxide semiconductor film is described as an example of a semiconductor device.

As illustrated in FIG. 1D, the transistor 410 includes a gate electrode 401, a gate insulating film 402, an oxide semiconductor film 403, a source electrode 405a, and a drain electrode 405b over a substrate 400 having an insulating surface. Over the oxide semiconductor film 403, a metal oxide film 407 having a function of preventing charging of the oxide semiconductor film 403 toward the back channel is provided.

FIG. 1A to FIG. 1D illustrate an example of a method for manufacturing the transistor 410.

First, after a conductive film is formed over the substrate 400 having an insulating surface, the gate electrode 401 is formed by a first photolithography process. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

There is no particular limitation on a substrate that can be used as the substrate 400 having an insulating surface as long as it has heat resistance enough to withstand heat treatment performed later. For example, a substrate such as a glass substrate, a ceramic substrate, a quartz substrate, or a sapphire substrate can be used. In addition, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be used as long as it has an insulating surface. The transistor 410 may be formed over the top.

Further, a flexible substrate may be used as the substrate 400. In the case of using a flexible substrate, the transistor 410 including the oxide semiconductor film 403 may be directly formed over the flexible substrate, or the transistor 410 including the oxide semiconductor film 403 may be formed over another manufacturing substrate. Thereafter, it may be peeled off and transferred to the flexible substrate. Note that in order to separate the transistor from the manufacturing substrate and transfer it to the flexible substrate, a separation layer may be provided between the manufacturing substrate and the transistor including the oxide semiconductor film.

Note that an insulating film serving as a base film may be provided between the substrate 400 and the gate electrode 401. The base film has a function of preventing diffusion of impurity elements from the substrate 400 and is formed using one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. Can do.

In addition, the gate electrode 401 may be formed using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing any of these materials as a single layer or a stacked layer. it can.

Next, a gate insulating film 402 is formed over the gate electrode 401. The gate insulating film 402 is formed using a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, a oxynitride oxide, using a plasma CVD method, a sputtering method, or the like. One or a plurality of films selected from an aluminum film or a hafnium oxide film can be used.

In addition, the oxide semiconductor film 403 in this embodiment is intrinsic (i) by removing impurities and highly purifying the impurity to be a carrier donor other than the main component of the oxide semiconductor. Type) or substantially intrinsic (i-type) oxide semiconductor is used. Specifically, for example, the hydrogen concentration of the oxide semiconductor film 403 is 5 × 10 ¹⁹ atoms / cm ³ or less, desirably 5 × 10 ¹⁸ atoms / cm ³ or less, and more desirably 5 × 10 ¹⁷ atoms / cm ³ or less. And Note that the hydrogen concentration in the oxide semiconductor film 403 is measured by secondary ion mass spectrometry (SIMS). As described above, in the oxide semiconductor film 403 in which the hydrogen concentration is sufficiently reduced to be highly purified, and the defect level in the energy gap due to oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is 1 It becomes less than x10 ¹² / cm ³ , desirably less than 1 × 10 ¹¹ / cm ³ , more desirably less than 1.45 × 10 ¹⁰ / cm ³ . For example, the off-current at room temperature (25 ° C.) (here, the value per unit channel width (1 μm)) is 100 zA (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA or less. In this manner, by using an i-type (intrinsic) or substantially i-type oxide semiconductor, the transistor 410 with extremely excellent off-state current characteristics can be obtained.

Since such a highly purified oxide semiconductor is extremely sensitive to interface states or interface charges, the interface between the oxide semiconductor film and the gate insulating film is important. Therefore, high quality is required for the gate insulating film in contact with the highly purified oxide semiconductor.

For example, high-density plasma CVD using μ waves (for example, a frequency of 2.45 GHz) is preferable as a method for manufacturing a gate insulating film because a high-quality insulating layer with high density and high withstand voltage can be formed. This is because when the highly purified oxide semiconductor and the high-quality gate insulating film are in close contact with each other, the interface state density can be reduced and interface characteristics can be improved.

Needless to say, other film formation methods such as a sputtering method and a plasma CVD method can be applied as long as a high-quality insulating film can be formed as the gate insulating film. Alternatively, an insulating film in which the film quality of the gate insulating film and the interface characteristics with the oxide semiconductor are modified by heat treatment after formation of the oxide semiconductor film may be used. In any case, any film can be used as long as it can reduce the interface state density with the oxide semiconductor and form a favorable interface as well as the quality of the gate insulating film.

In order to prevent hydrogen, a hydroxyl group, and moisture from being contained in the gate insulating film 402 and the oxide semiconductor film as much as possible, as a pretreatment for forming the oxide semiconductor film, the gate electrode 401 is formed in a preheating chamber of a sputtering apparatus. It is preferable to preheat the substrate 400 on which the substrate 400 is formed or the substrate 400 on which the gate insulating film 402 is formed to desorb impurities such as hydrogen and moisture adsorbed on the substrate 400 and exhaust them. Note that a cryopump is preferable as an exhaustion unit provided in the preheating chamber. Note that this preheating treatment can be omitted. Further, this preheating may be similarly performed on the substrate 400 (before the metal oxide film 407 is formed) formed up to the source electrode 405a and the drain electrode 405b in a later step.

Next, an oxide semiconductor film with a thickness of 3 nm to 30 nm is formed over the gate insulating film 402 by a sputtering method. If the thickness of the oxide semiconductor film is excessively large (for example, the thickness is 50 nm or more), the transistor may be normally on, and thus the above-described film thickness is preferable.

Note that before the oxide semiconductor film is formed by a sputtering method, reverse sputtering in which an argon gas is introduced to generate plasma is performed, so that powdery substances (particles and dust) attached to the surface of the gate insulating film 402 are formed. It is preferable to remove Reverse sputtering is a method of modifying the surface by forming a plasma near the substrate by applying a voltage using an RF power source on the substrate side in an argon atmosphere without applying a voltage to the target side. Note that nitrogen, helium, oxygen, or the like may be used instead of the argon atmosphere.

Examples of the oxide semiconductor used for the oxide semiconductor film include an In—Sn—Ga—Zn—O-based oxide semiconductor that is a quaternary metal oxide and an In—Ga—Zn—O that is a ternary metal oxide. Oxide semiconductor, In—Sn—Zn—O oxide semiconductor, In—Al—Zn—O oxide semiconductor, Sn—Ga—Zn—O oxide semiconductor, Al—Ga—Zn—O oxide Semiconductor, Sn-Al-Zn-O-based oxide semiconductor, binary metal oxide In-Zn-O-based oxide semiconductor, Sn-Zn-O-based oxide semiconductor, Al-Zn-O-based Oxide semiconductor, Zn-Mg-O-based oxide semiconductor, Sn-Mg-O-based oxide semiconductor, In-Mg-O-based oxide semiconductor, In-Ga-O-based oxide semiconductor, In-O-based oxidation A material semiconductor, a Sn-O-based oxide semiconductor, a Zn-O-based oxide semiconductor, or the like is used. Door can be. Further, the oxide semiconductor may contain SiO ₂ . Here, for example, an In—Ga—Zn—O-based oxide semiconductor means an oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn), and there is no particular limitation on the composition ratio thereof. Absent. Moreover, elements other than In, Ga, and Zn may be included.

As the oxide semiconductor film, a thin film represented by the chemical formula, InMO ₃ (ZnO) _m (m> 0) can be used. Here, M represents one or more metal elements selected from Ga, Al, Mn, and Co. For example, M includes Ga, Ga and Al, Ga and Mn, or Ga and Co.

In the case of using an In—Ga—Zn—O-based material as the oxide semiconductor, as a target to be used, for example, a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [molar ratio] The oxide target can be used. Without limitation to the material and the composition of the target, for _{example, In 2 O 3: Ga 2} O 3: ZnO = 1: 1: 2 may be an oxide target [mol ratio].

In the case where an In—Zn—O-based material is used as the oxide semiconductor, the composition ratio of the target used is an atomic ratio, and In: Zn = 50: 1 to 1: 2 (in terms of the molar ratio, In ₂ O ₃ : ZnO = 25: 1 to 1: 4), preferably In: Zn = 20: 1 to 1: 1 (In ₂ O ₃ : ZnO = 10: 1 to 1: 2 in terms of molar ratio), More preferably, In: Zn = 15: 1 to 1.5: 1 (In ₂ O ₃ : ZnO = 15: 2 to 3: 4 in terms of molar ratio). For example, a target used for forming an In—Zn—O-based oxide semiconductor satisfies Z> 1.5X + Y when the atomic ratio is In: Zn: O = X: Y: Z.

The filling rate of the target is 90% or more and 100% or less, preferably 95% or more and 99.9% or less. By using a target with a high filling rate, the formed oxide semiconductor film can be a dense film.

In this embodiment, the oxide semiconductor film is formed by a sputtering method using an In—Ga—Zn—O-based oxide target. The oxide semiconductor film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As a sputtering gas used for forming the oxide semiconductor film, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

The oxide semiconductor film is formed in such a manner that the substrate 400 is held in a deposition chamber kept under reduced pressure and the substrate temperature is 100 ° C. to 600 ° C., preferably 200 ° C. to 400 ° C. When the substrate 400 is formed while being heated, the concentration of impurities contained in the formed oxide semiconductor film can be reduced. Further, damage due to sputtering is reduced. Then, a sputtering gas from which hydrogen and moisture are removed is introduced while moisture remaining in the deposition chamber is removed, and an oxide semiconductor film is formed over the substrate 400 using the above target. In order to remove moisture remaining in the deposition chamber, it is preferable to use an adsorption-type vacuum pump such as a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. In the film formation chamber evacuated using a cryopump, for example, a compound containing a hydrogen atom (more preferably a compound containing a carbon atom) such as a hydrogen atom or water (H ₂ O) is exhausted. The concentration of impurities contained in the oxide semiconductor film formed in the chamber can be reduced.

As an example of the film forming conditions, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power source is 0.5 kW, and the oxygen (oxygen flow rate is 100%) atmosphere is applied. Note that a pulse direct current power source is preferable because powder substances (also referred to as particles or dust) generated in film formation can be reduced and the film thickness can be made uniform.

Next, the oxide semiconductor film is processed into an island-shaped oxide semiconductor film 441 by a second photolithography step (see FIG. 1A). Further, a resist mask for forming the island-shaped oxide semiconductor film 441 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used. Accordingly, an oxide semiconductor film in a region overlapping with the gate electrode can be formed over the gate insulating film.

Note that the etching of the oxide semiconductor film here may be either dry etching or wet etching, or both. For example, as an etchant used for wet etching of the oxide semiconductor film, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. In addition, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, a conductive film for forming a source electrode and a drain electrode (including a wiring formed using the same layer) is formed over the gate insulating film 402 and the oxide semiconductor film 441. As the conductive film used for the source electrode and the drain electrode, for example, a metal film containing an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, or a metal nitride film containing the above-described element as a component ( A titanium nitride film, a molybdenum nitride film, a tungsten nitride film, or the like can be used. Further, a refractory metal film such as Ti, Mo, W or the like or a metal nitride film thereof (titanium nitride film, molybdenum nitride film, tungsten nitride film) is provided on one or both of the lower side or the upper side of a metal film such as Al or Cu. It is good also as a structure which laminated | stacked. Further, the conductive film used for the source electrode and the drain electrode may be formed using a conductive metal oxide. Examples of the conductive metal oxide include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium oxide tin oxide alloy (In ₂ O ₃ —SnO ₂ , abbreviated as ITO), An indium oxide-zinc oxide alloy (In ₂ O ₃ —ZnO) or a metal oxide material containing silicon oxide can be used.

Note that the materials of the source electrode and the drain electrode are preferably determined in consideration of the electron affinity of the oxide semiconductor to be used and the electron affinity of the metal oxide film. That is, when the work function of the material of the source electrode and the drain electrode is W [eV], the electron affinity of the oxide semiconductor is φ ₁ [eV], and the electron affinity of the metal oxide film is φ ₂ [eV], φ ₂ +0 4 <W <(φ ₁ +0.5), preferably (φ ₂ +0.9) <W <(φ ₁ +0.4). For example, if materials having an electron affinity of 4.5 eV and 3.5 eV are used as the oxide semiconductor and the metal oxide film, respectively, the work function of the material of the source electrode and the drain electrode is larger than 3.9 eV. In addition, it is preferable to use a metal or a metal compound that is less than 5.0 eV, preferably greater than 4.4 eV and less than 4.9 eV. Thus, in the transistor 410, injection of electrons from the source electrode 405a and the drain electrode 405b to the metal oxide film 407 can be prevented, leakage current can be suppressed, and a junction between the oxide semiconductor film and the source and drain electrodes can be suppressed. Good electrical characteristics can be obtained. Examples of the material having such a work function include molybdenum nitride and tungsten nitride. These materials are preferable because they are excellent in heat resistance. From the above relational expression, a relational expression of φ ₂ <(φ ₁ +0.1), preferably φ ₂ <(φ ₁ −0.5) is derived. More preferably, φ ₂ <(φ ₁ -0.9) should be satisfied.

In the third photolithography step, a resist mask is formed over the conductive film used for the source electrode and the drain electrode, selectively etched to form the source electrode 405a and the drain electrode 405b, and then the resist mask is removed ( (See FIG. 1B).

Ultraviolet light, KrF laser light, or ArF laser light is preferably used for light exposure for forming the resist mask in the third photolithography process. The channel length L of a transistor to be formed later is determined by the distance between the lower end portion of the source electrode 405a and the lower end portion of the drain electrode 405b adjacent to each other on the oxide semiconductor film 441. Note that when exposure is performed with a channel length L of less than 25 nm, exposure at the time of forming a resist mask in the third photolithography process is performed using extreme ultraviolet (Extreme Ultraviolet) having a wavelength as short as several nm to several tens of nm. It is good to do. Exposure by extreme ultraviolet light has a high resolution and a large depth of focus. Therefore, the channel length L of a transistor to be formed later can be 10 nm to 1000 nm, and the operation speed of the circuit can be increased.

In order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that is an exposure mask in which transmitted light has a plurality of intensities. Good. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

Note that it is preferable that etching conditions be optimized so that the oxide semiconductor film 441 is not etched and divided when the conductive film used for the source electrode and the drain electrode is etched. However, it is difficult to obtain a condition that only the conductive film is etched and the oxide semiconductor film 441 is not etched at all. When the conductive film is etched, only part of the oxide semiconductor film 441 is etched, and a groove (concave portion) is obtained. In some cases, the oxide semiconductor film may include

In this embodiment, a Ti film is used as the conductive film used for the source electrode and the drain electrode, and an In—Ga—Zn—O-based oxide semiconductor is used for the oxide semiconductor film 441; 31 wt% hydrogen peroxide solution: 28 wt% ammonia water: water = 5: 2: 2) is used.

Next, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar may be performed to remove hydrogen, water, or the like attached to the exposed surface of the oxide semiconductor film. In the case where plasma treatment is performed, it is preferable to form the metal oxide film 407 in contact with part of the oxide semiconductor film 441 without exposure to the air following the plasma treatment.

Next, a metal oxide film 407 which covers the source electrode 405a and the drain electrode 405b and is in contact with part of the oxide semiconductor film 441 is formed (see FIG. 1C). Note that the thickness of the metal oxide film 407 is larger than that of the oxide semiconductor film 441. The metal oxide film 407 is a film that is in contact with the oxide semiconductor film 441 between the source electrode 405a and the drain electrode 405b on the back channel side of the oxide semiconductor film 441, and removes charges accumulated at the interface.

The charge accumulated in the source electrode 405a or the drain electrode 405b may move positive charge from the source electrode 405a or the drain electrode 405b to the oxide semiconductor film, and may be charged on the back channel side interface of the oxide semiconductor film. In particular, if the electrical conductivity of the oxide semiconductor film and the electrical conductivity of the material layer in contact with the back channel side of the oxide semiconductor film are different, the charge flows into the oxide semiconductor film, and the charge is trapped at the interface. Bonding with hydrogen in the physical semiconductor film becomes a donor center at the interface. This causes a problem that the characteristics of the transistor fluctuate. Therefore, both reduction of hydrogen in the oxide semiconductor film and prevention of charging of the oxide semiconductor film are important.

The difference between the band gap of the oxide semiconductor film and the band gap of the metal oxide film is preferably less than 3 eV. For example, when an In—Ga—Zn—O-based oxide semiconductor is used as the oxide semiconductor film and silicon oxide or aluminum oxide is used as the metal oxide film, the band gap of the In—Ga—Zn—O-based oxide semiconductor is used. Is 3.15 eV, and the band gap of silicon oxide and aluminum oxide is 8 eV, which may cause the above problem. In addition, when a film containing nitride (eg, a silicon nitride film) is used instead of the metal oxide film, the electrical conductivity of the oxide semiconductor film varies due to contact between the film containing nitride and the oxide semiconductor film. There is a risk.

Therefore, the metal oxide film 407 preferably has a property of quickly removing even if a positive charge is charged on the back channel side of the oxide semiconductor film. However, the material used for the metal oxide film 407 is a material whose hydrogen content is equal to or less than that of the oxide semiconductor film and is not more than one digit even when the content is higher than that of the oxide semiconductor film, The energy gap is preferably a material having a material that is equal to or more than the material of the oxide semiconductor film.

In one embodiment of the present invention, the case where a gallium oxide, for example, gallium oxide (GaOx (X> 0)) is used as the metal oxide film will be described. The physical properties of gallium oxide include, for example, a band gap of 3.0 eV to 5.2 eV (for example, 4.9 eV), a dielectric constant of 8 to 20, an electron affinity of 3.5 eV, and In—Ga—Zn—O. The physical property values of the system oxide semiconductor are, for example, a band gap of 3.15 eV, a dielectric constant of 15, and an electron affinity of 3.5 eV, and the physical property values of gallium oxide and In—Ga—Zn—O based oxide semiconductor. Since each difference is small, it is preferable. Further, since gallium oxide has a wide band gap of about 4.9 eV, it has translucency in the visible light region. Further, it is preferable to use gallium oxide as the metal oxide film because contact resistance between the In—Ga—Zn—O-based oxide semiconductor film and the gallium oxide film can be reduced. In the case of using gallium oxide as the metal oxide film, an In—Ga—Zn—O-based oxide semiconductor, an In—Ga—O-based oxide semiconductor, and a Ga—Zn—O-based oxide semiconductor are used as the oxide semiconductor material. Good.

In this manner, by using the metal oxide film having an antistatic function, accumulation of charges on the back channel side of the oxide semiconductor film can be suppressed. In addition, by providing the metal oxide film over the top surface of the oxide semiconductor film, even if a positive charge is charged on the back channel side of the oxide semiconductor film, the metal oxide film can be quickly removed. In addition, by using the metal oxide film 407, generation of a parasitic channel on the back channel side of the oxide semiconductor film 403 can be prevented. Accordingly, variation in electrical characteristics such as electrical conductivity of the oxide semiconductor film can be suppressed, so that the reliability of the transistor can be improved.

It is preferable to use a gallium oxide film as the metal oxide film. The gallium oxide film can be obtained by sputtering, CVD, vapor deposition, or the like. Although depending on the composition ratio of oxygen and gallium, the gallium oxide film has a band gap of about 4.9 eV and has translucency in the visible light region.

In this specification, gallium oxide may be expressed as GaOx (x> 0). For example, when GaOx has a crystal structure, Ga ₂ O ₃ where x = 1.5 is known.

In this embodiment, as the metal oxide film 407, a gallium oxide film obtained by a sputtering method using a pulsed direct current (DC) power supply is used. Note that a gallium oxide target is preferably used as a target for the sputtering method. The electric conductivity may be adjusted by adding indium or zinc as appropriate to the metal oxide film 407 in accordance with the electric conductivity of the oxide semiconductor film to be used. For example, a film containing 0.01 to 5 atomic% of indium or zinc is formed by a sputtering method using a target in which indium or zinc is added to gallium oxide. By adding indium or zinc, the electrical conductivity of the metal oxide film 407 is improved, and the electrical conductivity of the oxide semiconductor film 403 is made close to that, whereby charge accumulation can be further reduced.

In particular, when an In—Ga—Zn—O film is used as the oxide semiconductor film, a common gallium element is contained in GaOx used as the metal oxide film 407, which is preferable.

The metal oxide film 407 is preferably formed using a method in which impurities such as water and hydrogen are not mixed. When hydrogen is contained in the metal oxide film 407, penetration of the hydrogen into the oxide semiconductor film or extraction of oxygen in the oxide semiconductor film by hydrogen occurs, and the resistance of the back channel of the oxide semiconductor film is reduced (n There is a risk of forming a parasitic channel. Therefore, it is important not to use hydrogen in the deposition method so that the metal oxide film 407 contains as little hydrogen as possible.

In this embodiment, a gallium oxide film having a thickness of more than 10 nm and a thickness of the oxide semiconductor film 441 or more is formed as the metal oxide film 407 by a sputtering method. This is because the thickness of the metal oxide film 407 is increased to be greater than that of the oxide semiconductor film 441 so that the metal oxide film 407 can efficiently remove charges. The substrate temperature at the time of film formation may be from room temperature to 300 ° C. The gallium oxide film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As in the formation of the oxide semiconductor film, in order to remove moisture remaining in the deposition chamber of the metal oxide film 407, an adsorption-type vacuum pump (such as a cryopump) is preferably used. The concentration of impurities contained in the metal oxide film 407 formed in the film formation chamber evacuated using a cryopump can be reduced. Further, as an evacuation unit for removing moisture remaining in the deposition chamber of the metal oxide film 407, a turbo pump provided with a cold trap may be used.

As a sputtering gas used for forming the metal oxide film 407, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

The metal oxide film 407 may cover at least the channel formation region of the oxide semiconductor film, the source electrode 405a, and the drain electrode 405b, and the metal oxide film 407 may be selectively removed if necessary. Note that known wet etching or known dry etching can be used for etching the gallium oxide film used in this embodiment. For example, wet etching is performed using a hydrofluoric acid solution or nitric acid.

Next, heat treatment is performed on the oxide semiconductor film 441 in a state where the metal oxide film 407 and a part (channel formation region) are in contact with each other (see FIG. 1C).

The temperature of the heat treatment is 250 to 650 ° C., preferably 450 to 600 ° C., or less than the strain point of the substrate. For example, the substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor film is subjected to heat treatment at 450 ° C. for 1 hour in a nitrogen atmosphere.

Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element may be used. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used. Note that in the case where a GRTA apparatus is used as the heat treatment apparatus, since the heat treatment time is short, the substrate may be heated in an inert gas heated to a high temperature of 650 ° C. to 700 ° C.

The heat treatment may be performed in an atmosphere of nitrogen, oxygen, ultra-dry air (air with a water content of 20 ppm or less, preferably 1 ppm or less, preferably 10 ppb or less), or a rare gas (such as argon or helium). It is preferable that water, hydrogen, etc. are not contained in the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas. In addition, the purity of nitrogen, oxygen, or a rare gas introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0. 1 ppm or less).

Further, since heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 407 containing oxygen are in contact with each other, the oxide semiconductor film is one of the main components of the oxide semiconductor that is reduced at the same time due to the impurity removal step. Oxygen can be supplied from the metal oxide film 407 containing oxygen to the oxide semiconductor film. Accordingly, charge trapping centers in the oxide semiconductor film can be reduced. Through the above steps, a highly purified oxide semiconductor film 403 which is electrically i-type (intrinsic) is obtained. Further, by this heat treatment, impurities can be removed from the metal oxide film 407 at the same time, and the metal oxide film 407 can be highly purified.

In the highly purified oxide semiconductor film 403, the number of carriers derived from donors is extremely small, and the carrier concentration is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably 1 × 10 10. It is less than ¹¹ / cm ³ .

Through the above steps, the transistor 410 is formed (see FIG. 1D). The transistor 410 is a transistor including the oxide semiconductor film 403 which is purified by intentionally removing impurities such as hydrogen, moisture, a hydroxyl group, or a hydride (also referred to as a hydrogen compound) from the oxide semiconductor film. Thus, the transistor 410 has stable electrical characteristics and is electrically stable.

In addition to the above heat treatment, another heat treatment may be performed. For example, heat treatment (first heat treatment) may be performed after the oxide semiconductor film 441 is formed, and heat treatment (second heat treatment) may be performed after the metal oxide film 407 is formed. In this case, the first heat treatment can be, for example, a treatment in which heating is performed in an inert gas atmosphere and cooling is performed in an oxygen atmosphere (at least an atmosphere containing oxygen). By applying such first heat treatment, dehydration and oxidation of the oxide semiconductor film can be favorably performed.

Further, heat treatment may be further performed after the second heat treatment. For example, heat treatment may be performed at 100 ° C. to 200 ° C. for 1 hour to 30 hours in the air. This heat treatment may be performed while maintaining a constant heating temperature, or the temperature is raised from room temperature to a heating temperature of 100 ° C. or more and 200 ° C. or less, and the temperature lowering from the heating temperature to the room temperature is repeated several times. May be.

In addition, the transistor 410 including the oxide semiconductor film 403 can be driven at high speed because relatively high field-effect mobility can be obtained. Therefore, by using the transistor in the pixel portion, a high-quality image can be provided. In addition, since the driver circuit portion including the transistor including the highly purified oxide semiconductor film and the pixel portion can be formed over the same substrate, the number of components of the semiconductor device can be reduced.

In addition, in the transistor 410 including the metal oxide film 407, generation of a parasitic channel on the back channel side of the oxide semiconductor film 403 can be prevented. Further, by preventing the occurrence of a parasitic channel on the back channel side of the oxide semiconductor film 403 in the transistor 410, variation in threshold voltage can be suppressed; thus, a transistor with improved reliability can be obtained. .

By the way, in the transistor 410 illustrated in FIG. 1D, a two-layer dielectric of an oxide semiconductor film 403 and a metal oxide film 407 is provided in contact with each other. When two different dielectric layers are stacked, the first layer (the oxide semiconductor film 403 in the transistor 410) has a dielectric constant of ε ₁ , a conductivity of σ ₁ , a thickness of d ₁ , and a second layer ( In the transistor 410, when the dielectric constant of the metal oxide film 407) is ε ₂ , the conductivity is σ ₂ , and the thickness is d ₂ , the two-layer stack can be represented by the model diagram of FIG. Note that in FIG. 9A, S represents an area. Further, the model diagram of FIG. 9A can be replaced with the equivalent circuit of FIG. In the figure, C ₁ represents the capacitance value of the first layer, G ₁ represents the resistance value of the first layer, C ₂ represents the capacitance value of the second layer, and G ₂ represents the resistance value of the second layer. Here, when the voltage V is applied to the two layers, the charge Q represented by the following formula (1) is accumulated at the interface between the two layers after t seconds.

In the transistor 410 illustrated in FIG. 1D, the above-described interface where the charge Q is accumulated corresponds to the back channel side of the oxide semiconductor film 403, and the dielectric constant or electrical conductivity of the metal oxide film 407, or metal oxide By appropriately setting the thickness of the film 407, the charge Q accumulated at the interface on the back channel side can be reduced.

Here, when the formula (1) is modified, it is expressed by the following formula (2) and formula (3).

From Equations (2) and (3), the following four conditions (A) to (D) can be assumed to reduce the charge Q.
Condition (A) τ _i is made very large.
Condition (B) V ₂ is brought close to zero, that is, G ₂ is made much larger than G ₁ .
Condition (C) _{C 2} close to zero.
Condition (D) τ ₁ is brought close to τ ₂ .

Condition (A), in order to greatly increase the tau _{i is, τ i = (C 1 +} C 2) / a because _{(G 1 + G 2),} (C 1 + C 2) a _(G 1 ₊ G 2) It can be much larger. Here, since C ₁ and G ₁ are parameters of the oxide semiconductor film 403, C ₂ needs to be increased in order to reduce the charge Q by the metal oxide film 407. However, when the _{C 2} is increased by _{C 2} = epsilon ₂ S / _{d 2} than epsilon _2, Q becomes larger than the formula (2), resulting in inconsistency. That is, the charge Q cannot be adjusted by τ _i .

In order to bring V ₂ close to zero under the condition (B), it is only necessary to satisfy G ₂ >> G ₁ from Equation (3). Since G ₁ is a parameter of the oxide semiconductor film 403, it is necessary to increase G _{2 in} order to reduce the charge Q by the metal oxide film 407. Specifically, since G ₂ = σ ₂ S / d ₂ , a material having a small d ₂ or a large σ ₂ is selected. However, reduction of _{d 2} is, _{C 2} = _{C 2} is larger than epsilon ₂ S / _{d 2,} can not be employed conditions (A) and likewise for Q increases. Further, “σ ₂ is large” means that the metal oxide film 407 has a higher electrical conductivity than the oxide semiconductor film 403, and it cannot be employed because of the high risk of leakage current and short circuit.

In order to make C ₂ very small under the condition (C), d ₂ is made larger than C ₂ = ε ₂ S / d ₂ or a material having a small ε ₂ is selected.

In order to bring τ ₁ closer to τ _{2 under} the condition (D), τ ₁ = ε ₁ / σ ₁ and τ ₂ = ε ₂ / σ ₂ , so ε ₁ / σ ₁ ≈ε ₂ / σ _What is necessary is to select the film | membrane used as ₂ . This is equivalent to _{C 1 / G 1 ≒ C 2} / G 2.

Therefore, in order to effectively prevent the accumulation of the charge Q, the film thickness (d ₂ ) of the metal oxide film 407 is increased, or a material having a small dielectric constant (ε ₂ ) as the material of the metal oxide film 407, preferably It is preferable to select a material smaller than the oxide semiconductor film 403 (for example, a material having a dielectric constant ε of 8 to 20). Alternatively, a material having a physical property close to that of the oxide semiconductor film is made of metal so that ε ₁ / σ ₁ ≈ε ₂ / σ ₂ (ε ₁ is the dielectric constant of the oxide semiconductor and σ ₁ is the conductivity of the oxide semiconductor). It is preferable to select the oxide film.

As described above, in the transistor 410 including the metal oxide film 407 having an antistatic function, charge accumulation on the back channel side of the oxide semiconductor film can be suppressed. In addition, by providing the metal oxide film over the top surface of the oxide semiconductor film, even if a positive charge is charged on the back channel side of the oxide semiconductor film, the metal oxide film can be quickly removed. In addition, in the transistor 410 including the metal oxide film 407, generation of a parasitic channel on the back channel side of the oxide semiconductor film 403 can be prevented. Further, by preventing generation of a parasitic channel on the back channel side of the oxide semiconductor film in the transistor, variation in threshold voltage can be suppressed. Accordingly, fluctuations in the electrical conductivity of the oxide semiconductor film can be suppressed, so that the reliability of the transistor can be improved.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 2)
In this embodiment, another embodiment of a method for manufacturing a semiconductor device will be described. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example in which heat treatment is performed on the oxide semiconductor film before the metal oxide film 407 in contact with the oxide semiconductor film is formed in the manufacturing method of the transistor 410 described in Embodiment 1 will be described.

This heat treatment may be applied to the oxide semiconductor film before being processed into an island-shaped oxide semiconductor film as long as the metal oxide film 407 is formed after the oxide semiconductor film is formed. The present invention may be applied before or after the source electrode 405a and the drain electrode 405b are formed.

The temperature of the heat treatment is 250 to 650 ° C., preferably 450 to 600 ° C. For example, the substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor film is subjected to heat treatment at 450 ° C. for 1 hour in a nitrogen atmosphere. After the heat treatment, it is preferable to form a metal oxide film without exposure to the air and prevent re-mixing of water and hydrogen into the oxide semiconductor film.

Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element may be used. For example, an RTA apparatus such as a GRTA apparatus or an LRTA apparatus can be used. Note that in the case where a GRTA apparatus is used as the heat treatment apparatus, since the heat treatment time is short, the substrate may be heated in an inert gas heated to a high temperature of 650 ° C. to 700 ° C.

The heat treatment may be performed in an atmosphere of nitrogen, oxygen, ultra-dry air (air with a water content of 20 ppm or less, preferably 1 ppm or less, preferably 10 ppb or less), or a rare gas (such as argon or helium). It is preferable that water, hydrogen, etc. are not contained in the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas. Further, the purity of nitrogen, oxygen, or a rare gas introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm). Or less).

By this heat treatment, impurities such as moisture or hydrogen in the oxide semiconductor film can be reduced.

Furthermore, heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film containing oxygen are in contact with each other, so that the oxide semiconductor film is one of the main components of the oxide semiconductor that is reduced at the same time due to the impurity removal step. Oxygen can be supplied from the metal oxide film containing oxygen to the oxide semiconductor film.

Therefore, when heat treatment before the formation of the metal oxide film and heat treatment after the formation of the metal oxide film are performed on the oxide semiconductor film, impurities such as moisture and hydrogen are further desorbed. Intrinsic semiconductor) or an oxide semiconductor film close to i-type can be obtained.

Therefore, a transistor including a highly purified oxide semiconductor film has stable electrical characteristics with less variation in electrical characteristics.

In addition, in a transistor including a metal oxide film, generation of a parasitic channel on the back channel side of the oxide semiconductor film can be prevented.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 3)
A semiconductor device having a display function (also referred to as a display device) can be manufactured using any of the transistors described as examples in Embodiment 1 or 2. In addition, part or the whole of a driver circuit including a transistor can be formed over the same substrate as the pixel portion to form a system-on-panel.

In FIG. 2A, a sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and is sealed with the second substrate 4006. In FIG. 2A, a single crystal semiconductor film or a polycrystalline semiconductor film is formed over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. A scan line driver circuit 4004 and a signal line driver circuit 4003 are mounted. In addition, a variety of signals and potentials are supplied to a separately formed signal line driver circuit 4003, the scan line driver circuit 4004, and the pixel portion 4002 from FPCs (Flexible Printed Circuits) 4018a and 4018b.

In FIGS. 2B and 2C, a sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and the scan line driver circuit 4004. A second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Therefore, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with the display element by the first substrate 4001, the sealant 4005, and the second substrate 4006. 2B and 2C, a single crystal semiconductor film or a polycrystal is formed over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. A signal line driver circuit 4003 formed of a semiconductor film is mounted. In FIGS. 2B and 2C, a signal line driver circuit 4003 which is formed separately, and various signals and potentials which are supplied to the scan line driver circuit 4004 or the pixel portion 4002 are supplied from an FPC 4018.

2B and 2C illustrate an example in which the signal line driver circuit 4003 is separately formed and mounted on the first substrate 4001, the invention is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.

Note that a connection method of a driver circuit which is separately formed is not particularly limited, and a COG (Chip On Glass) method, a wire bonding method, a TAB (Tape Automated Bonding) method, or the like can be used. 2A illustrates an example in which the signal line driver circuit 4003 and the scanning line driver circuit 4004 are mounted by a COG method, and FIG. 2B illustrates an example in which the signal line driver circuit 4003 is mounted by a COG method. FIG. 2C illustrates an example in which the signal line driver circuit 4003 is mounted by a TAB method.

The display device includes a panel in which the display element is sealed, and a module in which an IC including a controller is mounted on the panel.

Note that a display device in this specification means an image display device, a display device, or a light source (including a lighting device). Further, an IC (integrated circuit) is directly mounted on a connector, for example, a module with an FPC or TAB tape or TCP attached, a module with a printed wiring board provided on the end of the TAB tape or TCP, or a display element by the COG method. All modules are included in the display device.

In addition, the pixel portion and the scan line driver circuit provided over the first substrate 4001 include a plurality of transistors, and the transistor shown as an example in Embodiment 1 or 2 can be used.

As a display element provided in the display device, a liquid crystal element (also referred to as a liquid crystal display element) or a light-emitting element (also referred to as a light-emitting display element) can be used. The light-emitting element includes, in its category, an element whose luminance is controlled by current or voltage, and specifically includes inorganic EL (Electro Luminescence), organic EL, and the like. In addition, a display medium whose contrast is changed by an electric effect, such as electronic ink, can be used.

One embodiment of a semiconductor device is described with reference to FIGS. 3 to 5 correspond to cross-sectional views taken along line MN in FIG.

As shown in FIGS. 3 to 5, the semiconductor device includes a connection terminal electrode 4015 and a terminal electrode 4016. The connection terminal electrode 4015 and the terminal electrode 4016 are connected to a terminal of the FPC 4018 and an anisotropic conductive film 4019. Are electrically connected.

The connection terminal electrode 4015 is formed using the same conductive film as the first electrode layer 4030, and the terminal electrode 4016 is formed using the same conductive film as the source and drain electrodes of the transistors 4010 and 4011.

The pixel portion 4002 and the scan line driver circuit 4004 provided over the first substrate 4001 each include a plurality of transistors. In FIGS. 3 to 5, the transistor 4010 included in the pixel portion 4002 and the scan line The transistor 4011 included in the driver circuit 4004 is illustrated. In FIG. 3, a metal oxide film 4020 having an antistatic function is provided over the transistors 4010 and 4011, and an insulating layer 4021 is further provided in FIGS. 4 and 5. Note that the insulating film 4023 is an insulating film functioning as a base film.

In this embodiment, as the transistor 4010 and the transistor 4011, the transistor described in any of Embodiments 1 and 2 can be used.

In the transistor 4010 and the transistor 4011, an oxide semiconductor film is an impurity such as hydrogen, moisture, a hydroxyl group, or hydride (also referred to as a hydrogen compound) by heat treatment after the metal oxide film 4020 stacked over the oxide semiconductor film is formed. Is an oxide semiconductor film which is intentionally excluded from the oxide semiconductor film and is highly purified.

In addition, since heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 4020 containing oxygen are in contact with each other, the oxide semiconductor film is one of the main components of the oxide semiconductor that is reduced at the same time due to the impurity removal step. Oxygen can be supplied from the metal oxide film 4020 containing oxygen to the oxide semiconductor film. Therefore, the oxide semiconductor film is more purified and electrically i-type (intrinsic).

Therefore, the transistor 4010 and the transistor 4011 including the highly purified oxide semiconductor film are electrically stable because variation in electrical characteristics is suppressed. Therefore, a highly reliable semiconductor device can be provided as the semiconductor device of this embodiment illustrated in FIGS.

In addition, in a transistor including a metal oxide film having an antistatic function, generation of a parasitic channel on the back channel side of the oxide semiconductor film can be prevented. Further, by preventing generation of a parasitic channel on the back channel side of the oxide semiconductor film in the transistor, variation in threshold voltage can be suppressed.

In this embodiment, a conductive layer may be provided on the metal oxide film so as to overlap with a channel formation region of the oxide semiconductor film of the transistor 4011 for the driver circuit. By providing the conductive layer so as to overlap with the channel formation region of the oxide semiconductor film, the amount of change in the threshold voltage of the transistor 4011 before and after the BT test can be further reduced. In addition, the potential of the conductive layer may be the same as or different from that of the gate electrode of the transistor 4011, and the conductive layer can function as a second gate electrode. Further, the potential of the conductive layer may be GND, 0 V, or a floating state.

The conductive layer also has a function of shielding an external electric field, that is, preventing the external electric field from acting on the inside (a circuit portion including a thin film transistor) (particularly, an electrostatic shielding function against static electricity). With the shielding function of the conductive layer, the electrical characteristics of the transistor can be prevented from changing due to the influence of an external electric field such as static electricity.

A transistor 4010 provided in the pixel portion 4002 is electrically connected to a display element to form a display panel. The display element is not particularly limited as long as display can be performed, and various display elements can be used.

FIG. 3 shows an example of a liquid crystal display device using a liquid crystal element as a display element. In FIG. 3, a liquid crystal element 4013 which is a display element includes a first electrode layer 4030, a second electrode layer 4031, and a liquid crystal layer 4008. Note that an insulating film 4032 and an insulating film 4033 functioning as alignment films are provided so as to sandwich the liquid crystal layer 4008. The second electrode layer 4031 is provided on the second substrate 4006 side, and the first electrode layer 4030 and the second electrode layer 4031 are stacked with the liquid crystal layer 4008 interposed therebetween.

Reference numeral 4035 denotes a columnar spacer obtained by selectively etching the insulating film, and is provided for controlling the film thickness (cell gap) of the liquid crystal layer 4008. A spherical spacer may be used.

When a liquid crystal element is used as the display element, a thermotropic liquid crystal, a low molecular liquid crystal, a polymer liquid crystal, a polymer dispersed liquid crystal, a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or the like can be used. These liquid crystal materials exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, and the like depending on conditions.

Alternatively, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. The blue phase is one of the liquid crystal phases. When the temperature of the cholesteric liquid crystal is increased, the blue phase appears immediately before the transition from the cholesteric phase to the isotropic phase. Since the blue phase appears only in a narrow temperature range, in order to improve the temperature range, a liquid crystal composition mixed with 5% by weight or more of a chiral agent is used for the liquid crystal layer. A liquid crystal composition containing a liquid crystal exhibiting a blue phase and a chiral agent has a response speed as short as 1 msec or less and is optically isotropic, so alignment treatment is unnecessary and viewing angle dependence is small. Further, since it is not necessary to provide an alignment film, a rubbing process is not required, so that electrostatic breakdown caused by the rubbing process can be prevented, and defects or breakage of the liquid crystal display device during the manufacturing process can be reduced. . Therefore, the productivity of the liquid crystal display device can be improved. In a transistor using an oxide semiconductor film, the electrical characteristics of the transistor may fluctuate significantly due to the influence of static electricity and deviate from the design range. Therefore, it is more effective to use a blue phase liquid crystal material for a liquid crystal display device including a transistor including an oxide semiconductor film.

The specific resistivity of the liquid crystal material is 1 × 10 ⁹ Ω · cm or more, preferably 1 × 10 ¹¹ Ω · cm or more, and more preferably 1 × 10 ¹² Ω · cm or more. In addition, the value of the specific resistivity in this specification shall be the value measured at 20 degreeC.

The size of the storage capacitor provided in the liquid crystal display device is set so that charges can be held for a predetermined period in consideration of a leakage current of a transistor arranged in the pixel portion. By using a transistor including a high-purity oxide semiconductor film, it is sufficient to provide a storage capacitor having a capacity of 1/3 or less, preferably 1/5 or less of the liquid crystal capacity of each pixel. .

In the transistor including the highly purified oxide semiconductor film used in this embodiment, the current value in an off state (off-state current value) can be reduced. Therefore, the holding time of an electric signal such as an image signal can be increased, and the writing interval can be set longer in the power-on state. Therefore, since the frequency of the refresh operation can be reduced, there is an effect of suppressing power consumption.

In addition, the transistor including the highly purified oxide semiconductor film used in this embodiment can have a relatively high field-effect mobility and can be driven at high speed. Therefore, a high-quality image can be provided by using the transistor in the pixel portion of the liquid crystal display device. In addition, since the driver circuit portion including the transistor and the pixel portion can be formed over the same substrate, the number of components of the liquid crystal display device can be reduced.

The liquid crystal display device includes a TN (Twisted Nematic) mode, an IPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching) mode, an ASM (Axially Symmetrical Micro-cell) mode, and an OCB mode. An FLC (Ferroelectric Liquid Crystal) mode, an AFLC (Anti Ferroelectric Liquid Crystal) mode, or the like can be used.

Alternatively, a normally black liquid crystal display device such as a transmissive liquid crystal display device employing a vertical alignment (VA) mode may be used. Here, the vertical alignment mode is a type of method for controlling the alignment of liquid crystal molecules of the liquid crystal display panel, and is a method in which the liquid crystal molecules are oriented in the vertical direction with respect to the panel surface when no voltage is applied. There are several examples of the vertical alignment mode. For example, an MVA (Multi-Domain Vertical Alignment) mode, a PVA (Patterned Vertical Alignment) mode, an ASV mode, and the like can be used. Further, a method called multi-domain or multi-domain design in which pixels (pixels) are divided into several regions (sub-pixels) and molecules are tilted in different directions can be used.

In the display device, a black matrix (light shielding layer), a polarizing member, a retardation member, an optical member (an optical substrate) such as an antireflection member, and the like are provided as appropriate. For example, circularly polarized light using a polarizing substrate and a retardation substrate may be used. Further, a backlight, a sidelight, or the like may be used as the light source.

In addition, a time division display method (field sequential drive method) can be performed using a plurality of light emitting diodes (LEDs) as a backlight. By applying the field sequential driving method, color display can be performed without using a color filter.

As a display method in the pixel portion, a progressive method, an interlace method, or the like can be used. Further, the color elements controlled by the pixels when performing color display are not limited to three colors of RGB (R represents red, G represents green, and B represents blue). For example, there is RGBW (W represents white) or RGB in which one or more colors of yellow, cyan, magenta, etc. are added. The size of the display area may be different for each dot of the color element. However, this embodiment is not limited to a display device for color display, and can also be applied to a display device for monochrome display.

In addition, as a display element included in the display device, a light-emitting element utilizing electroluminescence can be used. A light-emitting element using electroluminescence is distinguished depending on whether the light-emitting material is an organic compound or an inorganic compound. Generally, the former is called an organic EL element and the latter is called an inorganic EL element.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are respectively injected from the pair of electrodes into the layer containing the light emitting organic compound, and a current flows. Then, these carriers (electrons and holes) recombine, whereby the light-emitting organic compound forms an excited state, and emits light when the excited state returns to the ground state. Due to such a mechanism, such a light-emitting element is referred to as a current-excitation light-emitting element.

Inorganic EL elements are classified into a dispersion-type inorganic EL element and a thin-film inorganic EL element depending on the element structure. The dispersion-type inorganic EL element has a light-emitting layer in which particles of a light-emitting material are dispersed in a binder, and the light emission mechanism is donor-acceptor recombination light emission using a donor level and an acceptor level. The thin-film inorganic EL element has a structure in which a light emitting layer is sandwiched between dielectric layers and further sandwiched between electrodes, and the light emission mechanism is localized light emission utilizing inner-shell electron transition of metal ions. Here, a case where an organic EL element is used as the light emitting element will be described.

In order to extract light emitted from the light-emitting element, at least one of the pair of electrodes may be transparent. Then, a transistor and a light emitting element are formed over the substrate, and a top emission that extracts light from a surface opposite to the substrate, a bottom emission that extracts light from a surface on the substrate side, and a surface opposite to the substrate side and the substrate. There is a light-emitting element having a dual emission structure in which light emission is extracted from the light-emitting element, and any light-emitting element having an emission structure can be applied.

FIG. 4 illustrates an example of a light-emitting device using a light-emitting element as a display element. A light-emitting element 4513 which is a display element is electrically connected to a transistor 4010 provided in the pixel portion 4002. Note that although the structure of the light-emitting element 4513 is a stacked structure of the first electrode layer 4030, the electroluminescent layer 4511, and the second electrode layer 4031, it is not limited to the structure shown. The structure of the light-emitting element 4513 can be changed as appropriate depending on the direction in which light is extracted from the light-emitting element 4513, or the like.

A partition wall 4510 is formed using an organic insulating material or an inorganic insulating material. In particular, a photosensitive resin material is preferably used so that an opening is formed over the first electrode layer 4030 and the side wall of the opening has an inclined surface formed with a continuous curvature.

The electroluminescent layer 4511 may be composed of a single layer or a plurality of layers stacked.

A protective film may be formed over the second electrode layer 4031 and the partition wall 4510 so that oxygen, hydrogen, moisture, carbon dioxide, or the like does not enter the light-emitting element 4513. As the protective film, a silicon nitride film, a silicon nitride oxide film, a DLC film, or the like can be formed. In addition, a filler 4514 is provided in a space sealed by the first substrate 4001, the second substrate 4006, and the sealant 4005 and sealed. Thus, it is preferable to package (enclose) with a protective film (bonded film, ultraviolet curable resin film, etc.) or a cover material that has high air tightness and little degassing so as not to be exposed to the outside air.

In addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used as the filler 4514. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicone resin, PVB (polyvinyl chloride) Butyl) or EVA (ethylene vinyl acetate) can be used. For example, nitrogen may be used as the filler.

If necessary, an optical film such as a polarizing plate, a circular polarizing plate (including an elliptical polarizing plate), a retardation plate (λ / 4 plate, λ / 2 plate), a color filter, or the like is provided on the light emitting element exit surface. You may provide suitably. Further, an antireflection film may be provided on the polarizing plate or the circularly polarizing plate. For example, anti-glare treatment can be performed that diffuses reflected light due to surface irregularities and reduces reflection.

In addition, as a display device, electronic paper that drives electronic ink can be provided. Electronic paper is also called an electrophoretic display device (electrophoretic display), and has the same readability as paper, low power consumption compared to other display devices, and the advantage that it can be made thin and light. ing.

The electrophoretic display device may have various forms, and a plurality of microcapsules including first particles having a positive charge and second particles having a negative charge are dispersed in a solvent or a solute. By applying an electric field to the microcapsule, the particles in the microcapsule are moved in opposite directions to display only the color of the particles assembled on one side. Note that the first particle or the second particle contains a dye and does not move in the absence of an electric field. In addition, the color of the first particles and the color of the second particles are different (including colorless).

As described above, the electrophoretic display device is a display using a so-called dielectrophoretic effect in which a substance having a high dielectric constant moves to a high electric field region.

A solution in which the above microcapsules are dispersed in a solvent is referred to as electronic ink. This electronic ink can be printed on a surface of glass, plastic, cloth, paper, or the like. Color display is also possible by using particles having color filters or pigments.

Note that the first particle and the second particle in the microcapsule are a conductor material, an insulator material, a semiconductor material, a magnetic material, a liquid crystal material, a ferroelectric material, an electroluminescent material, an electrochromic material, or a magnetophoresis. A kind of material selected from the materials or a composite material thereof may be used.

In addition, a display device using a twisting ball display system can be used as the electronic paper. The twist ball display method is a method in which spherical particles separately painted in white and black are arranged between a first electrode layer and a second electrode layer which are electrode layers used for a display element, and the first electrode layer and the second electrode layer are arranged. In this method, a potential difference is generated in the two electrode layers to control the orientation of the spherical particles.

FIG. 5 illustrates active matrix electronic paper as one embodiment of a semiconductor device. The electronic paper in FIG. 5 is an example of a display device using a twisting ball display system.

A black region 4615a and a white region 4615b are provided between the first electrode layer 4030 connected to the transistor 4010 and the second electrode layer 4031 provided for the second substrate 4006, and the periphery is filled with a liquid. A spherical particle 4613 including a cavity 4612 is provided, and the periphery of the spherical particle 4613 is filled with a filler 4614 such as a resin. The second electrode layer 4031 corresponds to a common electrode (counter electrode). The second electrode layer 4031 is electrically connected to the common potential line.

3 to 5, as the first substrate 4001 and the second substrate 4006, a flexible substrate can be used in addition to a glass substrate. For example, a light-transmitting plastic substrate or the like can be used. Can be used. As the plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a polyester film, or an acrylic resin film can be used. A sheet having a structure in which an aluminum foil is sandwiched between PVF films or polyester films can also be used.

In addition, the metal oxide film 4020 not only prevents the generation of a parasitic channel on the back channel side of the oxide semiconductor film, but also decreases from the oxide semiconductor film at the same time by the removal process of impurities such as hydrogen, moisture, hydroxyl, or hydride. It also has a function of supplying oxygen to the oxide semiconductor film.

As the metal oxide film 4020, a gallium oxide film formed by a sputtering method may be used. Alternatively, a film in which indium or zinc is added to gallium oxide may be used. For example, a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc can be used. By adding indium or zinc, the electrical conductivity of the metal oxide film 4020 can be improved, and charge accumulation can be further reduced.

The insulating layer 4021 can be formed using an inorganic insulating material or an organic insulating material. Note that an organic insulating material having heat resistance such as acrylic resin, polyimide, benzocyclobutene resin, polyamide, or epoxy resin is preferably used as the planarization insulating film. In addition to the organic insulating material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus glass), or the like can be used. Note that the insulating layer may be formed by stacking a plurality of insulating films formed using these materials.

The formation method of the insulating layer 4021 is not particularly limited, and according to the material, sputtering method, spin coating method, dipping method, spray coating, droplet discharge method (ink jet method, screen printing, offset printing, etc.), roll coating Curtain coating, knife coating, etc. can be used.

The display device performs display by transmitting light from a light source or a display element. Therefore, thin films such as a substrate, an insulating film, and a conductive film provided in the pixel portion where light is transmitted have light-transmitting properties with respect to light in the visible wavelength region.

In the first electrode layer 4030 and the second electrode layer 4031 (also referred to as a pixel electrode layer, a common electrode layer, a counter electrode layer, and the like) that apply voltage to the display element, the direction of light to be extracted and the position where the electrode layer is provided The light transmitting property and the reflecting property may be selected depending on the pattern structure of the electrode layer.

The first electrode layer 4030 and the second electrode layer 4031 include indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, and indium. A light-transmitting conductive material such as tin oxide (hereinafter referred to as ITO), indium zinc oxide, or indium tin oxide to which silicon oxide is added can be used.

The first electrode layer 4030 and the second electrode layer 4031 are tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta). , Chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), silver (Ag), or other metals, or alloys thereof, or One or more kinds of nitrides can be used.

Alternatively, the first electrode layer 4030 and the second electrode layer 4031 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof can be given.

In addition, since the transistor is easily broken by static electricity or the like, it is preferable to provide a protective circuit for protecting the driving circuit. The protection circuit is preferably configured using a non-linear element.

As described above, by using the transistor described in Embodiment 1 or 2, a semiconductor device having various functions can be provided.

(Embodiment 4)
A semiconductor device having an image sensor function of reading information on an object can be manufactured using the transistor whose example is described in any of Embodiments 1 and 2.

FIG. 6A illustrates an example of a semiconductor device having an image sensor function. FIG. 6A is an equivalent circuit of the photosensor, and FIG. 6B is a cross-sectional view illustrating part of the photosensor.

In the photodiode 602, one electrode is electrically connected to the photodiode reset signal line 658 and the other electrode is electrically connected to the gate of the transistor 640. In the transistor 640, one of a source and a drain is electrically connected to the photosensor reference signal line 672, and the other of the source and the drain is electrically connected to one of the source and the drain of the transistor 656. The transistor 656 has a gate electrically connected to the gate signal line 659 and the other of the source and the drain electrically connected to the photosensor output signal line 671.

Note that in a circuit diagram in this specification, a symbol of a transistor using an oxide semiconductor film is described as “OS” so that the transistor can be clearly identified as a transistor using an oxide semiconductor film. In FIG. 6A, a transistor 640 and a transistor 656 are transistors each using an oxide semiconductor film.

FIG. 6B is a cross-sectional view illustrating the photodiode 602 and the transistor 640 in the photosensor. The photodiode 602 and the transistor 640 functioning as a sensor are provided over a substrate 601 (TFT substrate) having an insulating surface. Yes. A substrate 613 is provided over the photodiode 602 and the transistor 640 by using an adhesive layer 608.

A metal oxide film 631 having an antistatic function, an interlayer insulating layer 633, and an interlayer insulating layer 634 are provided over the transistor 640. The photodiode 602 is provided over the interlayer insulating layer 633, and from the interlayer insulating layer 633 side between the electrode layer 641 formed over the interlayer insulating layer 633 and the electrode layer 642 provided over the interlayer insulating layer 634. The first semiconductor layer 606a, the second semiconductor layer 606b, and the third semiconductor layer 606c are sequentially stacked.

In the transistor 640, the oxide semiconductor film is subjected to heat treatment, so that impurities such as hydrogen, moisture, a hydroxyl group, or hydride (also referred to as a hydrogen compound) are intentionally removed from the oxide semiconductor film and purified. Oxide semiconductor film.

In addition, since heat treatment is performed in a state where the oxide semiconductor film and the metal oxide film 631 containing oxygen are in contact with each other, the oxide semiconductor film is one of the main components of the oxide semiconductor that is reduced at the same time due to the impurity removal step. Oxygen can be supplied from the metal oxide film 631 containing oxygen to the oxide semiconductor film. Therefore, the oxide semiconductor film is more purified and electrically i-type (intrinsic).

Therefore, the transistor 640 including the highly purified oxide semiconductor film is electrically stable because variation in electrical characteristics is suppressed. Therefore, a highly reliable semiconductor device can be provided as the semiconductor device of this embodiment.

The electrode layer 641 is electrically connected to the conductive layer 643 formed in the interlayer insulating layer 634, and the electrode layer 642 is electrically connected to the gate electrode 645 through the electrode layer 644. The gate electrode 645 is electrically connected to the gate electrode of the transistor 640, and the photodiode 602 is electrically connected to the transistor 640.

Here, a semiconductor layer having p-type conductivity as the first semiconductor layer 606a, a high-resistance semiconductor layer (i-type semiconductor layer) as the second semiconductor layer 606b, and an n-type conductivity as the third semiconductor layer 606c. A pin type photodiode in which a semiconductor layer having the same is stacked is illustrated.

The first semiconductor layer 606a is a p-type semiconductor layer and can be formed using an amorphous silicon film containing an impurity element imparting p-type conductivity. The first semiconductor layer 606a is formed by a plasma CVD method using a semiconductor material gas containing a Group 13 impurity element (eg, boron (B)). Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. Alternatively, after an amorphous silicon film not containing an impurity element is formed, the impurity element may be introduced into the amorphous silicon film by a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by introducing an impurity element by an ion implantation method or the like and then performing heating or the like. In this case, as a method for forming the amorphous silicon film, an LPCVD method, a vapor phase growth method, a sputtering method, or the like may be used. The first semiconductor layer 606a is preferably formed to have a thickness greater than or equal to 10 nm and less than or equal to 50 nm.

The second semiconductor layer 606b is an i-type semiconductor layer (intrinsic semiconductor layer) and is formed using an amorphous silicon film. For the formation of the second semiconductor layer 606b, an amorphous silicon film is formed by a plasma CVD method using a semiconductor material gas. Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. The second semiconductor layer 606b may be formed by an LPCVD method, a vapor deposition method, a sputtering method, or the like. The second semiconductor layer 606b is preferably formed to have a thickness greater than or equal to 200 nm and less than or equal to 1000 nm.

The third semiconductor layer 606c is an n-type semiconductor layer and is formed using an amorphous silicon film containing an impurity element imparting n-type conductivity. The third semiconductor layer 606c is formed by a plasma CVD method using a semiconductor material gas containing a Group 15 impurity element (eg, phosphorus (P)). Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. Alternatively, after an amorphous silicon film not containing an impurity element is formed, the impurity element may be introduced into the amorphous silicon film by a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by introducing an impurity element by an ion implantation method or the like and then performing heating or the like. In this case, as a method for forming the amorphous silicon film, an LPCVD method, a vapor phase growth method, a sputtering method, or the like may be used. The third semiconductor layer 606c is preferably formed to have a thickness of 20 nm to 200 nm.

Further, the first semiconductor layer 606a, the second semiconductor layer 606b, and the third semiconductor layer 606c may be formed using a polycrystalline semiconductor instead of an amorphous semiconductor, or may be formed using a microcrystalline (Semi Amorphous Semiconductor: SAS)) may be formed using a semiconductor.

A microcrystalline semiconductor belongs to a metastable state between an amorphous state and a single crystal state in consideration of Gibbs free energy. That is, it is a semiconductor having a third state that is stable in terms of free energy, and has a short-range order and lattice distortion. Columnar or needle-like crystals grow in the normal direction with respect to the substrate surface. Microcrystalline silicon which is a typical example of a microcrystalline semiconductor has a Raman spectrum shifted to a lower wave number side than 520 cm ⁻¹ indicating single crystal silicon. That is, the peak of the Raman spectrum of microcrystalline silicon is between 520 cm ⁻¹ indicating single crystal silicon and 480 cm ⁻¹ indicating amorphous silicon. Further, at least 1 atomic% or more of hydrogen or halogen is contained to terminate dangling bonds. Further, by adding a rare gas element such as helium, argon, krypton, or neon to further promote lattice distortion, stability can be improved and a good microcrystalline semiconductor film can be obtained.

This microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method with a frequency of several tens to several hundreds of MHz or a microwave plasma CVD apparatus with a frequency of 1 GHz or more. Typically, a silicon-containing gas such as SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , or SiF ₄ can be formed by diluting with hydrogen. Further, in addition to hydrogen, a microcrystalline semiconductor film can be formed by diluting a silicon-containing gas with one or more kinds of rare gas elements selected from helium, argon, krypton, and neon. The flow rate ratio of hydrogen to the silicon-containing gas at these times is 5 to 200 times, preferably 50 to 150 times, and more preferably 100 times. Furthermore, hydrocarbon gas such as CH ₄ and C ₂ H ₆ , germanium-containing gas such as GeH ₄ and GeF ₄ , F _{2, and the} like may be mixed in the silicon-containing gas.

Further, since the mobility of holes generated by the photoelectric effect is smaller than the mobility of electrons, the pin type photodiode exhibits better characteristics when the p type semiconductor layer side is the light receiving surface. Here, an example in which light 622 received by the photodiode 602 from the surface of the substrate 601 on which the pin-type photodiode is formed is converted into an electric signal. Further, since light from the semiconductor layer side having the opposite conductivity type to the semiconductor layer side as the light receiving surface becomes disturbance light, the electrode on the semiconductor layer side having the opposite conductivity type to the semiconductor layer side as the light receiving surface A conductive film having a light shielding property is preferably used for the layer. The n-type semiconductor layer side can also be used as the light receiving surface.

As the metal oxide film 631, a gallium oxide film formed by a sputtering method may be used. Alternatively, a film in which indium or zinc is added to gallium oxide may be used. For example, a gallium oxide film containing 0.01 to 5 atomic% of indium or zinc can be used. By adding indium or zinc, the electrical conductivity of the metal oxide film 631 can be improved, and charge accumulation can be further reduced.

As the interlayer insulating layers 633 and 634, an insulating layer functioning as a planarization insulating film is preferable in order to reduce surface unevenness. As the interlayer insulating layers 633 and 634, for example, an organic insulating material such as polyimide, acrylic resin, benzocyclobutene resin, polyamide, or epoxy resin can be used. In addition to the organic insulating material, a single layer or a stacked layer such as a low dielectric constant material (low-k material), a siloxane-based resin, PSG (phosphorus glass), or BPSG (phosphorus boron glass) can be used.

As the interlayer insulating layer 633 and the interlayer insulating layer 634, an insulating material is used. Depending on the material, a sputtering method, a spin coating method, a dipping method, a spray coating method, a droplet discharge method (an inkjet method, screen printing, an offset method). Printing), roll coating, curtain coating, knife coating and the like.

By detecting the light 622 incident on the photodiode 602, information on the object to be detected can be read. Note that a light source such as a backlight can be used when reading information on the object to be detected.

As the transistor 640, the transistor whose example is described in Embodiment 1 or 2 can be used. A transistor including a highly purified oxide semiconductor film in which impurities such as hydrogen, moisture, a hydroxyl group, or hydride (also referred to as a hydrogen compound) are intentionally removed from the oxide semiconductor film has a change in electrical characteristics of the transistor. Suppressed and electrically stable. In addition, in a transistor including a metal oxide film having an antistatic function, generation of a parasitic channel on the back channel side of the oxide semiconductor film can be prevented. Further, by preventing generation of a parasitic channel on the back channel side of the oxide semiconductor film in the transistor, variation in threshold voltage can be suppressed. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 5)
The liquid crystal display device disclosed in this specification can be applied to a variety of electronic devices (including game machines). Examples of the electronic device include a television device (also referred to as a television or a television receiver), a monitor for a computer, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (a mobile phone or a mobile phone). Large-sized game machines such as portable game machines, portable information terminals, sound reproduction apparatuses, and pachinko machines. Examples of electronic devices each including the liquid crystal display device described in the above embodiment will be described.

FIG. 7A illustrates an e-book reader (also referred to as an E-book), which can include a housing 9630, a display portion 9631, operation keys 9632, a solar cell 9633, and a charge / discharge control circuit 9634. The electronic book illustrated in FIG. 7A includes a function for displaying various information (still images, moving images, text images, and the like), a function for displaying a calendar, date, time, and the like on the display portion, and information displayed on the display portion. And a function for controlling processing by various software (programs). Note that FIG. 7A illustrates a structure including a battery 9635 and a DCDC converter (hereinafter abbreviated as a converter) 9636 as an example of the charge / discharge control circuit 9634. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion 9631, a highly reliable e-book reader can be obtained.

With the structure illustrated in FIG. 7A, when a transflective or reflective liquid crystal display device is used as the display portion 9631, use in a relatively bright situation is expected. In addition, the battery 9635 can be charged efficiently, which is preferable. Note that the solar cell 9633 can be provided as appropriate in an empty space (front surface or back surface) of the housing 9630; thus, the solar battery 9633 is preferable because the battery 9635 can be efficiently charged. Note that as the battery 9635, when a lithium ion battery is used, there is an advantage that reduction in size can be achieved.

The structure and operation of the charge / discharge control circuit 9634 illustrated in FIG. 7A will be described with reference to a block diagram in FIG. FIG. 7B illustrates the solar battery 9633, the battery 9635, the converter 9636, the converter 9637, the switches SW1 to SW3, and the display portion 9631. The battery 9635, the converter 9636, the converter 9637, and the switches SW1 to SW3 are charged and discharged. The location corresponds to the control circuit 9634.

First, an example of operation in the case where power is generated by the solar battery 9633 using external light is described. The power generated by the solar battery 9633 is boosted or lowered by the converter 9636 so that the voltage for charging the battery 9635 is obtained. When power from the solar cell 9633 is used for the operation of the display portion 9631, the switch SW1 is turned on, and the converter 9637 increases or decreases the voltage required for the display portion 9631. In the case where display on the display portion 9631 is not performed, the battery 9635 may be charged by turning off SW1 and turning on SW2.

Next, an example of operation in the case where power is not generated by the solar cell 9633 using external light will be described. The power stored in the battery 9635 is boosted or lowered by the converter 9637 by turning on the switch SW3. Then, power from the battery 9635 is used for the operation of the display portion 9631.

Note that although the solar cell 9633 is illustrated as an example of a charging unit, a configuration in which the battery 9635 is charged by another unit may be used. Moreover, it is good also as a structure performed combining another charging means.

FIG. 8A illustrates a laptop personal computer, which includes a main body 3001, a housing 3002, a display portion 3003, a keyboard 3004, and the like. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion 3003, a highly reliable laptop personal computer can be provided.

FIG. 8B illustrates a personal digital assistant (PDA). A main body 3021 is provided with a display portion 3023, an external interface 3025, operation buttons 3024, and the like. There is a stylus 3022 as an accessory for operation. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion 3023, a highly reliable personal digital assistant (PDA) can be provided.

FIG. 8C illustrates an example of an electronic book. For example, the electronic book includes two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are integrated with a shaft portion 2711 and can be opened / closed using the shaft portion 2711 as an axis. With such a configuration, an operation like a paper book can be performed.

A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. By adopting a configuration that displays different screens, for example, text is displayed on the right display unit (display unit 2705 in FIG. 8C) and an image is displayed on the left display unit (display unit 2707 in FIG. 8C). Can be displayed. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion 2705 and the display portion 2707, a highly reliable electronic book can be obtained.

FIG. 8C illustrates an example in which the housing 2701 is provided with an operation portion and the like. For example, the housing 2701 is provided with a power supply 2721, operation keys 2723, a speaker 2725, and the like. Pages can be turned with the operation keys 2723. Note that a keyboard, a pointing device, or the like may be provided on the same surface as the display portion of the housing. In addition, an external connection terminal (such as an earphone terminal or a USB terminal), a recording medium insertion portion, or the like may be provided on the rear surface or side surface of the housing. Further, the electronic book may have a structure as an electronic dictionary.

Further, the electronic book may have a configuration capable of transmitting and receiving information wirelessly. It is also possible to adopt a configuration in which desired book data or the like is purchased and downloaded from an electronic book server wirelessly.

FIG. 8D illustrates a mobile phone, which includes two housings, a housing 2800 and a housing 2801. The housing 2801 is provided with a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, an external connection terminal 2808, and the like. The housing 2800 is provided with a solar cell 2810 for charging the mobile phone, an external memory slot 2811, and the like. An antenna is incorporated in the housing 2801. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display panel 2802, a highly reliable mobile phone can be provided.

Further, the display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which are displayed as images is illustrated by dashed lines in FIG. Note that a booster circuit for boosting the voltage output from the solar battery cell 2810 to a voltage required for each circuit is also mounted.

In the display panel 2802, the display direction can be appropriately changed depending on a usage pattern. In addition, since the camera lens 2807 is provided on the same surface as the display panel 2802, a videophone can be used. The speaker 2803 and the microphone 2804 can be used for videophone calls, recording and playing sound, and the like as well as voice calls. Further, the housing 2800 and the housing 2801 can be slid to be in an overlapped state from the developed state as illustrated in FIG. 8D, and can be reduced in size to be portable.

The external connection terminal 2808 can be connected to an AC adapter and various types of cables such as a USB cable, and charging and data communication with a personal computer are possible. Further, a recording medium can be inserted into the external memory slot 2811 so that a larger amount of data can be stored and moved.

In addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.

FIG. 8E illustrates a digital video camera which includes a main body 3051, a display portion (A) 3057, an eyepiece portion 3053, operation switches 3054, a display portion (B) 3055, a battery 3056, and the like. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion (A) 3057 and the display portion (B) 3055, a highly reliable digital video camera can be obtained.

FIG. 8F illustrates an example of a television set. In the television device 9600, a display portion 9603 is incorporated in a housing 9601. Images can be displayed on the display portion 9603. Here, a structure in which the housing 9601 is supported by a stand 9605 is illustrated. By applying the semiconductor device described in any of Embodiments 1 to 4 to the display portion 9603, a highly reliable television device can be provided.

The television device 9600 can be operated with an operation switch provided in the housing 9601 or a separate remote controller. Further, the remote controller may be provided with a display unit that displays information output from the remote controller.

Note that the television set 9600 is provided with a receiver, a modem, and the like. General TV broadcasts can be received by a receiver, and connected to a wired or wireless communication network via a modem, so that it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between each other or between recipients).

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

400 substrate 401 gate electrode 402 gate insulating film 403 oxide semiconductor film 405a source electrode 405b drain electrode 407 metal oxide film 410 transistor 431 metal oxide film 441 oxide semiconductor film 601 substrate 602 photodiode 606a semiconductor layer 606b semiconductor layer 606c semiconductor layer 608 Adhesive layer 613 Substrate 631 Metal oxide film 633 Interlayer insulating layer 634 Interlayer insulating layer 640 Transistor 641 Electrode layer 642 Electrode layer 643 Conductive layer 644 Electrode layer 645 Gate electrode 656 Transistor 658 Photodiode reset signal line 659 Gate signal line 671 Photosensor output signal Line 672 Photosensor reference signal line 2701 Case 2703 Case 2705 Display portion 2707 Display portion 2711 Shaft portion 2721 Power supply 2723 Operation key 2725 Speaker 2800 Housing 2801 Housing 2802 Display panel 2803 Speaker 2804 Microphone 2805 Operation key 2806 Pointing device 2807 Camera lens 2808 External connection terminal 2810 Solar cell 2811 External memory slot 3001 Body 3002 Body 3003 Display unit 3004 Keyboard 3021 Body 3022 Stylus 3023 Display unit 3024 Operation button 3025 External interface 3051 Main body 3053 Eyepiece unit 3054 Operation switch 3055 Display unit (B)
3056 Battery 3057 Display part (A)
4001 Substrate 4002 Pixel portion 4003 Signal line driver circuit 4004 Scan line driver circuit 4005 Sealing material 4006 Substrate 4008 Liquid crystal layer 4010 Transistor 4011 Transistor 4013 Liquid crystal element 4015 Connection terminal electrode 4016 Terminal electrode 4018 FPC
4018a FPC
4018b FPC
4019 Anisotropic conductive film 4020 Metal oxide film 4021 Insulating layer 4023 Insulating film 4030 Electrode layer 4031 Electrode layer 4032 Insulating film 4033 Insulating film 4510 Partition 4511 Light emitting element 4513 Light emitting element 4514 Filler 4612 Cavity 4613 Spherical particle 4614 Filler 4615a Black Region 4615b White region 9600 Television apparatus 9601 Housing 9603 Display portion 9605 Stand 9630 Housing 9631 Display portion 9632 Operation key 9633 Solar cell 9634 Charge / discharge control circuit 9635 Battery 9636 Converter 9637 Converter

Claims (12)

A gate electrode;
A gate insulating film covering the gate electrode;
An oxide semiconductor film in a region overlapping with the gate electrode on the gate insulating film;
A source electrode and a drain electrode in contact with the oxide semiconductor film;
A metal oxide film in contact with the oxide semiconductor film and covering the source electrode and the drain electrode;
A semiconductor device.   The semiconductor device according to claim 1, wherein the metal oxide film includes gallium oxide.   The semiconductor device according to claim 2, wherein the metal oxide film includes 0.01 to 5 atomic% of indium or zinc.   The semiconductor device according to claim 1, wherein the oxide semiconductor film includes indium and gallium.   5. The semiconductor device according to claim 1, wherein each of the source electrode and the drain electrode includes a conductive material having a work function of 3.9 eV or more.   The semiconductor device according to claim 5, wherein the conductive material having a work function of 3.9 eV or more is tungsten nitride or titanium nitride.   The semiconductor device according to claim 1, wherein a difference between a band gap of the metal oxide film and a band gap of the oxide semiconductor film is less than 3.0 eV. Forming a gate electrode on the substrate;
Forming a gate insulating film covering the gate electrode;
Forming an oxide semiconductor film in a region overlapping with the gate electrode through the gate insulating film;
Forming a source electrode and a drain electrode on the oxide semiconductor film;
Forming a metal oxide film covering the oxide semiconductor film, the source electrode and the drain electrode;
A method for manufacturing a semiconductor device in which heat treatment is performed.   The method for manufacturing a semiconductor device according to claim 8, wherein a film containing gallium oxide is formed as the metal oxide film.   The method for manufacturing a semiconductor device according to claim 9, wherein a film containing 0.01 to 5 atomic% of indium or zinc is formed as the metal oxide film.   The method for manufacturing a semiconductor device according to claim 8, wherein the oxide semiconductor film is formed using a film containing indium and gallium.   The method for manufacturing a semiconductor device according to claim 8, wherein a temperature of the heat treatment is set to 450 ° C. or higher and 600 ° C. or lower.